Saturday 17 December 2011 19.05 EST
First published on Saturday 17 December 2011 19.05 EST

In an early scene of The Inbetweeners Movie, released in August, audiences met a central character wearing boxer shorts and scuba-diving equipment, noisily pleasuring himself into an open packet of wafer-thin ham. There followed 90 minutes of similarly vulgar surprises (intercourse with the elderly, the nasal ingestion of poo), but the film's biggest shock, its most convention-rattling stunner, was saved until last. Within a month of release, The Inbetweeners Movie – a feature-length spin-off of a sitcom broadcast on E4 from 2008 to 2010 – had become the most successful British comedy in cinema history.

And it doesn't, because their film was released on the same day as Hollywood blockbuster Cowboys & Aliens, starring proven money-maker Daniel Craig. A week later, the adaptation of David Nicholls's mega-selling novel One Day was due out. A Justin Timberlake vehicle, Friends With Benefits, hovered, as did new versions of Jane Eyre, Conan the Barbarian and The Smurfs…

The Inbetweeners should have been swamped by Hollywood mulch; instead, it spent four mind-blowingly lucrative weeks at the top of the summer charts. It out-earned Cowboys & Aliens nearly 8:1 in its opening weekend, taking £13m. A further £13m came in from the US box office, and to date, without accounting for inevitably chunky sales of the new DVD, the film has pulled in more than £45m. How did this happen?

"The show's writers [and creators, Iain Morris and Damon Beesley] must have suspected that there was a market for a British take on an American Pie, a Superbad," says Bird. "And they were right. Probably beyond their wildest dreams." Buckley agrees. "There was room for a young-British-lads film, and maybe we were the guys to do it."

Thomas wonders if the giant numbers the film registered might have been down to fans of the TV show – which was pulling in more than 3m viewers by the time its third series finished last year – going along to the cinema, each dragging several friends. Harrison thinks there was simply something "quintessentially British" about the film's depiction of a hopeless Mediterranean holiday, all sunburn and disappointment and failures to pull, that tapped in to domestic sympathies. Anyway, the thing was a triumph, and the question of a sequel looms.

"No one's asked me," says Buckley. "We haven't had one conversation about it," says Bird. "I think there will definitely be interested parties who will want to do it," says Thomas. "If we're being completely honest, the distributors will want to do more," says Harrison, "because it's money in the bank. Because they know, now, that we've got an audience for it." Thomas: "I love working with the rest of the cast and would always want to do something more." Bird: "I wouldn't rule it out. We'll wait and see."

Everyone agrees that if they're going to do it "the story has to be right". In other words: ready the wafer-thin ham.

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